This invention relates generally to semiconductor integrated circuits, and more particularly, to systems and methods for reducing noise in mixed-mode semiconductor integrated circuits.
In today""s environment, semiconductors may contain both analog and digital components, commonly referred to as mixed signal or mixed-mode integrated circuits (ICs). The integration of analog and digital components on the same chip reduces costs, area and power requirements, which are important considerations in the manufacture of ICs. However, the combination of analog and digital components on the same substrate causes design challenges. Principally, switching noise from high-speed digital circuits easily interfere with and damage high-frequency analog circuits. Normally digital circuits switch quickly between predefined voltage levels, and consequently induce transient noise in power lines. Analog circuits what operate at a multiplicity of voltage levels and frequencies are sensitive to induced noise while the digital circuits are better able to withstand interference from induced noise.
Integrated circuits include a number of devices that are noise sensitive high performance devices. Fast changes in the charging or discharging of current can cause drops in voltage. This transient voltage can be large enough to interfere with the performance of these sensitive devices.
Substrate noise can affect numerous applications. For instance, substrate noise is a problem with phase-locked loop systems (PLLs) and inverters. PLLs are used in numerous applications including data recovery in disk drives, wired and wireless communications, high-speed microprocessors and memories.
Invertors (also referred to as flip-flops) are also widely used. Flip-flops serve important functions in reading and writing bits of words in memory devices. Normally, flip-flops encompass high-speed switching circuits that can be addressed to write or read into the flip-flop (need to define the flip-flop)
In a steady-state or quiescent condition, i.e. no switching occurring between output states, no current flows in the flip-flop from a power supply. Typically, the flip-flop includes a network of transistors connected to a power source and ground. In the steady-state condition, one transistor (or group of transistors) is turned on, and another transistor (or group of transistors) is turned off. To switch from one transistor to another, the power source switches from one state to another, for instance, from low to high which draws current. When one transistor is being turned off and the other transistor is being turned on, for a period of time, both transistors are on. During this period high current is present in the network. This high current causes a spike in voltage which introduces noise during the switching process. As the current is pulled through wires in the network, resistance is encountered and the voltage begins to drop and becomes a transient voltage throughout the IC. These transients can propagate along wires supplying power to the integrated circuit from the printed circuit board on which the integrated circuit board is mounted. The transients produce radio frequency (RF) radiation which can interfere with proper operation of other circuits on the printed circuit board as well as other circuits within the integrated circuit itself.
A number of prior attempts at solving switching noise problems have been proposed. One proposed solution focuses on controlling the current surge. U.S. Pat. No. 5,905,339 entitled xe2x80x9cCMOS integrated circuit regulator for reducing power supply noise,xe2x80x9d issued May 18, 1999, involves a complementary metal-oxide-semiconductor (CMOS) regulator which provides a constant current to a set of logic gates during the switching transition. This arrangement decouples the external supply shared by analog circuits and supplies current to supply rails. This current is kept nearly constant by a clamping action of clamping transistors. Excess charge for transient currents is supplied by a capacitor, which is replenished during non-switching times.
Another attempt to solve the noise problem involves the addition of decoupling capacitors placed near active devices. The decoupling capacitors stabilize the current flowing to these devices. However, while the capacitor absorbs some of the voltage, a spike still occurs.
Still another attempt to solve substrate noise problems involves an active method utilizing linear feedback loops. This approach involves sampling the noise at the analog receiver portion of the noise and directing that noise into an input stage of a negative feedback loop. After being amplified with reverse phase, the noise is re-injected into the substrate again. The re-injected noise, which has the opposite phase to that of the original noise traveling inside the substrate, may be used to cancel up to 83% of the original noise. This solution operates on mixed-mode integrated circuits operating at lower frequencies and low power portable electronics with slower digital clock speeds.
Yet another attempt to manage switching noise involve partitioning analog and digital functions. This process requires unique manufacturing processes and custom designs. For example, U.S. Pat. No. 6,020,614 entitled xe2x80x9cMethod of Reducing Substrate Noise Coupling in Mixed Signal Integrated Circuits,xe2x80x9d issued Feb. 1, 2000, suggests that noise can be reduced by establishing boundary zones between the analog and digital circuits of a semiconductor substrate with the analog circuit having a separate power supply bus from the digital circuit. Further, this patent discloses providing interconnect signal lines such that the isolated wires between the circuits may functionally interact with other circuits while the substrate noise coupling from other circuits remains low. However, spacing the analog components from the digital components can waste precious semiconductor space, which is an important consideration in integrated circuit design.
Still another attempt to resolve switching noise problems is addressed in U.S. Pat. No. 5,649,160 entitled xe2x80x9cNoise Reduction in Integrated Circuits and Circuit Assemblies,xe2x80x9d issued Jul. 15, 1997. This patent suggests that the noise can be reduced by shaping the noise from the digital circuit and concentrating it in a single or a small number of parts of the frequency spectrum. This solution relies on the concept that the presence of noise in the analog circuit is less important at certain frequencies, and therefore the spectral peak or peaks from the digital circuit can be carefully placed to result in little or no interference.
The various prior attempts to solve the switching noise problems each have limitations. According, a need exists for systems and method to substantially reduce switching noise in mixed-mode integrated circuits.
This invention aims to overcome the problems associated with switching noise encountered in integrated circuits having analog and digital components by inclusion of a micro-battery on the integrated circuit. Noise arises in integrated circuits through several environments. Notably, noise is encountered when certain integrated circuits, such as inverters, transition from one logic state to another logic state. For example, inverter A must be turned on and inverter B must be turned off During the transition, for a period of time when both inverters are on while the transition completes. In this instance, a high current exists resulting in a spike in voltage and the introduction of noise.
An integrated circuit consistent with this invention that reduces switching noise includes an inverter network having at least two transistors, a gating network coupled to the inverter network, a micro-battery coupled to the inverter and a resistor coupled at one end to the micro-battery and connected to a power source at the other end. At steady state, the micro-battery is uncharged. When charged, nominal current flows through the micro-battery. When the inverter transitions, and the current surge occurs causing the resultant voltage spike, the current demand to reduce the voltage is drawn from the micro-battery. Thus, the integrated circuit avoids have a peak voltage flowing to and disrupting the analog components. In addition, the battery recharges gradually so no voltage spike occurs. Further, components of the integrated circuit are isolated from the power line, i.e. VDD, by the resistor that limits the current drawn on the line. Alternatively, the inverter can encompass a bipolar RAM storage cell including two crosscoupled three-emitter transistors.
In another embodiment of this invention, switching noise is reduced in a non-switched integrated circuit. This embodiment includes a plurality of transistors with one group of transistors in an on logic state and another group of transistors in an off logic state. A micro-battery couples to each group of transistors. Knowledge of status of transistors is determined by whether the associated micro-battery is charged or uncharged. To write to the cell, the associated micro-battery is charged, turning on the accompanying transistor.
Another alternative embodiment of this invention to reduce switching noise encompasses a random access memory network having a micro-battery and resistor for reducing switching noise. The random access memory network includes a plurality cells. The cells encompass an inverter circuit. The addition of the micro-battery provides for the capacitor 130 charging from the micro-battery. Thus the capacitor is able to handle current surges resulting in the voltage spike to the power line. The resistor serves to further limit the current draw on the voltage line.
Yet another alternative embodiment of this invention includes a random access memory network with a micro-battery and resistor circuit associated with each cell of the network where each micro-battery and resistor circuit operates independently. A localized micro-battery source for each cell increases the speed of the network while reducing switching noise and resistor size.
This invention accordingly aims to achieve at least one, more or combinations of the following objectives:
To provide systems and methods for reducing switching noise of a mixed-mode integrated circuit such that components of an integrated circuit are not damaged by transient noise.
To provide systems and methods for reducing switching noise of an integrated circuit utilizing a micro-battery to supply current to the integrated circuit upon an increase in current demands during period of transition from one logic state to another logic.
To provide systems and methods for use of a micro-battery in integrated circuits to indicate whether associated transistors are turned off or turned on.
To provide systems and methods for reducing switching noise in integrated circuits utilizing a micro-battery that efficiently uses semiconductor space.
To provide systems and methods that isolate power lines from voltage spikes.
Other objects, advantages and features of the systems and methods of this invention will be set forth in part in the description which follows and in part will be obvious from the description or may be learned by practice of the invention. The objects, advantages and features of this invention will be realized and attained by means of the elements and combinations particularly pointed out in the claims.